The present invention relates generally to reciprocating piston engines and more particularly, but not exclusively, to internal combustion engines of such a type.
At the present time the great majority of engines which provide power for motor vehicles are reciprocating piston engines in which the pistons and their connecting rods rotate a crankshaft.
Since most internal combustion engines of the reciprocating piston type can, within limits, provide a greater power output for their weight at higher speeds of revolution than at lower ones, the emphasis in the development of such engines has for many years been on increasing the permissible working speed of the most critical element in this regard, namely the crankshaft.
Reasonably well-balanced crankshafts for high speed engines have required a lengthy development period, and even with the sophisticated mass production techniques of today are still a highly critical and expensive element of the engine which is a determining factor in its maximum working speed and cost. At high speeds the main bearings of the crankshaft and the connecting rod bearings are subjected to enormous stresses which result in substantial frictional losses, with resultant heating and greatly increased wear. The magnitude and effect of such stresses are discussed in detail in numerous technical publications and well known.
The back-and-forth pivoting of the connecting rods relative to the piston as one end of the rods follows the cranks of the crankshaft is the source of a further significant frictional loss arising from the resulting oscillating tilting torque on the pistons which presses the piston skirts against the cylinder wall. At high engine speeds particularly, the force of the pistons against the rod end is so great that the friction between the piston and the cylinder wall resulting from this tilting torque is increased dramatically, and the pistons and cylinder walls can be subjected to severe wear. Even at normal working speeds, this friction results in a substantial reduction in power. Furthermore, the oscillating tilting torque on the piston sets up vibrations in the cylinder walls which contribute a large part of the total noise from the engine.
The above problems are avoided with gas turbines and other types of engines, such as the Wankel engine, for example, which do not use a crankshaft. Gas turbine engines, however, have proved too costly for use in ordinary passenger cars, while the Wankel engine has certain other disadvantages.
There are also known reciprocating piston engines which avoid the use of a crankshaft. One such engine, for example, is what may be referred to as a reciprocating piston beam engine. In this engine, one or a pair of pistons are connected to the end of one arm of a pivoted beam to cause the end of the beam arm to oscillate back and fourth. The end of the other arm of the beam can then be used to drive a load back and forth, as for a pump, or even to rotate an output shaft by means of an eccenter mechanism. By choosing the distance between the pivot of the beam and the end where it is driven by the pistons to be sufficiently long, the oscillating tilting torque on the pistons can be greatly decreased. Also, by connecting the arm end to the center of a connecting rod rigidly connecting two opposing pistons, the tilting torque on the pistons can be effectively eliminated, since they then act as a single very long piston and provide a large mechanical advantage against the torque. Beam engines have been developed with the pistons being powered by steam pressure or by internal combustion. However, such known beam engines have thus far not been capable of working at a high speed, because of either balancing or lubrication difficulties.
A reciprocating piston beam engine having a high enough power-to-weight ratio to be feasible for use in ordinary mass-produced passenger automobiles must be capable of continuous operation at high speeds while minimizing at such speeds the effects of friction and vibration, without requiring for this substantially greater cost of manufacture than for present engines.